New bank systems that settle payments the same day allow "heists to occur in seconds from thousands of miles away," a security experts tells the Wall Street Journal. (AP Photo/Mark Lennihan)

(Newser)
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The FBI is investigating a cyberattack on Citigroup that cost the bank tens of millions of dollars, according to government officials. The theft—which Citi denies ever happened—was aimed at Citigroup's Citibank subsidiary and was carried out by hackers linked to a Russian gang, officials tell the Wall Street Journal.

The attackers' sophisticated arsenal included large numbers of hijacked computers infected with software called Black Energy, insiders say. "We had no breach of the system and there were no losses, no customer losses, no bank losses," a Citi exec says. Banks, however, are notoriously loathe to admit any security breaches for fear of frightening customers away, the Journal notes.